CN110915227B

CN110915227B - Separate inserting structure

Info

Publication number: CN110915227B
Application number: CN201780087434.1A
Authority: CN
Inventors: 卜勤练; 张蔚青; 付成鹏; 艾伦·索尔海姆; 乔立杰
Original assignee: Gc Fortonix; Accelink Technologies Co Ltd
Current assignee: Accelink Technologies Co Ltd
Priority date: 2016-12-27
Filing date: 2017-12-27
Publication date: 2022-06-28
Anticipated expiration: 2037-12-27
Also published as: EP3563586A4; US11296810B2; WO2018119521A1; CN110915227A; EP3563586A1; US20190349111A1; EP3563586B1; FI3563586T3

Abstract

An optical circuit, comprising: a multicast selection (MCS) switch and a plurality of optically selective devices coupled to output ports of the MCS switch. The selective device may select a single optical channel by blocking some wavelengths of light from passing therethrough and passing at least one other wavelength of light therethrough. The selective device may be a wave trap or a tunable filter. The optical circuit further includes an array of optical amplifiers, where each amplifier has an input port optically coupled to one of the selective devices. At least some of the amplifiers have a pump light port for receiving at least a portion of pump light from one or more laser pumps or from another optical amplifier, wherein the pump light is capable of providing sufficient pump light to fully saturate all rare-earth doped fibers in the array.

Description

Separate inserting structure

Technical Field

The present invention relates to optical communication systems, and in particular to a reconfigurable optical add/drop module.

Background

The increasing demand for data requires further increases in the capacity of optical communication systems, including the number of wavelengths supported per fiber and the data rate per wavelength. Optical channels are typically routed using reconfigurable optical add/drop modules (ROADMs). ROADM systems are currently designed to implement or facilitate colorless, directionless and contentionless (CDC) features. A non-directional characteristic may be understood as the ability to route wavelengths across any feasible path in the network, a colorless characteristic may be understood as the ability to receive any wavelength on any port, and a collision-free characteristic allows for adding or dropping duplicate wavelengths. However, a full CDC requires a very large number of transmitters and receivers, and the industry uses the term "CDC" to include nearly colorless, directionless, and conflict-free ROADMs. To achieve or further approach complete CDC, it is desirable to support as many transmitters and receivers as possible for the same number of add/drop ports.

The conventional CDC add/drop architecture is designed to add and drop a single wavelength channel. However, to increase the capacity of each transceiver, the industry is moving towards transmitters that support a super channel, which may have a wider channel bandwidth or include multiple wavelengths transmitted by a single transmitter.

It is therefore desirable to provide a high performance, cost-effective CDC add-drop architecture that meets the practical requirements of collision-free, directional-free, and colorless multiplexing for both single wavelength channels and superchannels.

Disclosure of Invention

According to one aspect of the invention, an optical system is provided that includes a first drop-side optical circuit. The first drop-side optical circuit includes: a multicast selection (MCS) switch having a plurality of input ports and a plurality of output ports; a plurality of selective devices, each selective device for blocking light of some wavelengths from passing therethrough and for passing light of at least one other wavelength therethrough to provide an output to an output port of the selective device, wherein each of the plurality of selective devices has an input port optically coupled to an output port of the MCS switch; and an optical amplification array comprising a plurality of optical amplifiers, each optical amplifier having an input port optically coupled to one of the selective devices for receiving an optical signal to be amplified, wherein each of the plurality of optical amplifiers comprises one or more rare-earth doped optical fibers and has an output port for providing an amplified optical signal, the optical fibers for amplifying the optical signal propagating therethrough. The optical amplification array comprises one or more laser pumps for providing pump light sufficient to fully saturate all rare earth doped fibers in the optical amplification array; wherein the number of the one or more laser pumps is less than the number of the plurality of optical amplifiers. Each of at least some of the optical amplifiers has a pump light port for receiving at least a portion of the pump light from the one or more laser pumps or from other optical amplifiers.

According to another aspect of the present invention, there is provided an optical system including a first drop-side optical circuit. The first drop-side optical circuit includes: a multicast select switch having a plurality of input ports and a plurality of output ports; and a plurality of selective devices, each selective device for blocking light of some wavelengths from passing therethrough and for passing light of at least one other wavelength therethrough to provide an output to an output port of the selective device, wherein each of the plurality of selective devices has an input port optically coupled to one of the plurality of output ports of the MCS switch. The selectivity device may be a tunable filter or a wave blocker. One or more gain flattening filters may be used for distributed gain balancing along each optical path in the first drop-side optical circuit. The optical system may also include a power-splitting circuit and a second drop-side optical circuit, wherein one or more of the input ports of an MCS switch of the second drop-side optical circuit are coupled to one or more of the output ports of the power-splitting circuit. The optical system may include an add-on side-light circuit.

According to yet another aspect of the present invention there is provided an optical system comprising an add-side optical circuit, wherein the add-side optical circuit comprises an add-side optical amplification array comprising a plurality of optical amplifiers, each optical amplifier having an input port for receiving an optical signal to be amplified. Each of the optical amplifiers includes one or more rare-earth doped optical fibers for amplifying an optical signal propagating therethrough and has an output port for providing an amplified optical signal. The insertion-side optical amplification array comprises one or more laser pumps for providing pump light to all rare-earth doped fibers in the insertion-side optical amplification array, wherein the number of the one or more laser pumps in the insertion-side optical amplification array is smaller than the number of the plurality of optical amplifiers in the insertion-side optical amplification array. Each of at least some of the optical amplifiers in the insertion-side optical amplification array has a pump-light port for receiving at least a portion of the pump light from one or more laser pumps of the insertion-side optical amplification array or from another of the optical amplifiers of the insertion-side optical amplification array.

The add-on sidelight circuit further comprises: a plurality of add-side selective devices, each for blocking the passage of some wavelengths of light therethrough and for passing at least one other wavelength of light therethrough to provide an output to an output port of the selective device, wherein each of the plurality of add-side selective devices has an input port optically coupled to the output port of one of the plurality of amplifiers in the add-side optically amplified array; and an add-side multicast select switch having a plurality of input ports and a plurality of output ports, wherein each of the plurality of input ports is optically coupled to an output port of one of the plurality of add-side selective devices.

Drawings

Exemplary embodiments will now be described with reference to the accompanying drawings, in which:

FIG. 1 is a node diagram illustrating a selection and selection architecture;

FIG. 2 is a node diagram illustrating a broadcast and selection architecture;

FIG. 3 is a ROADM functional diagram;

FIG. 4 illustrates an embodiment of an add/drop module;

FIG. 5 is a schematic diagram of an MCS switch;

fig. 6 is a schematic diagram of an exemplary embodiment of an add/drop module.

FIG. 7 is a plot of an EDFA gain spectrum;

FIG. 8 is a schematic diagram of a drop-out side distributed amplifier;

FIG. 9 is a schematic diagram of one embodiment of an insertion side distributed amplifier;

FIG. 10 is a schematic view of an enlarged array;

FIG. 11 is a schematic diagram of one embodiment of an insertion side amplification array;

fig. 12 is a schematic diagram of an amplifier array based on the use of a single saturating pump.

Detailed Description

The add/drop system disclosed herein may be used in place of the conventional add/drop module 30 shown in fig. 1 and 2.

Fig. 1 shows a selection and selection architecture comprising 2 degree ROADM nodes (i.e. with 2 possible directions available for routing wavelengths on the multiplex or line side). Of course, 2 degrees (degree) is used for illustrative purposes only, and ROADM nodes may have higher degrees. The node comprises a Wavelength Selective Switch (WSS) block 11, an add/drop block 30, a transmitter 42 and a receiver 41, the transmitter 42 and the receiver 41 together also being denoted TR 40. WSS block 11 includes line-side input and output

optical amplifiers

15 and 16 and WSS 20, WSS 20 may route line-side wavelengths to add/drop structure 30 or to another line direction. The add/drop block 30 includes a wavelength multiplexer/demultiplexer block 31 and an optical amplifier 32 for overcoming losses associated with the wavelength multiplexer/demultiplexer block.

Fig. 2 shows an alternative node architecture, namely a broadcast and select architecture, in which WSS demultiplexer 20 is replaced by a power splitter 120.

Referring to fig. 3, add/drop module 230 is a CDC or a near-CDC ROADM. It is desirable that the add/drop module 230 provide as much add/drop capacity as possible, meet CDC requirements as much as possible, and be able to work with both the selection and selection architecture shown in fig. 1 and the broadcast and selection architecture shown in fig. 2, in other words, with the WSS block 11 (fig. 1) or the WSS/distribution block (split block) 12 (fig. 2). Also, the degree of

modules

11 and 12 need not be 2, but may vary. An input optical beam, which is a portion of the light transmitted through the optical communication system, is provided to the drop side of the module 230 for further selection of the desired wavelength or wavelengths. On the add-in side, module 230 provides one or more beams of light into the communication system. In this and other scenarios, the light beam may be a guided light beam or a non-guided light beam.

Fig. 4 illustrates an embodiment of an add/drop system 230 disclosed herein, the add/drop system 230 also referred to as an add/drop module 230. The left side of the figure shows the insert function and the right side shows the drop function.

The drop side may include an optional distribution circuit 380 and one or more switching circuits 381. In one embodiment, the distribution circuit 380 includes a power divider 321, the power divider 321 having one input port and a plurality of output ports. The distributor 321 is a 1 × N distributor; for example, N may be 2, 4 or 8. In operation, the input port of the splitter receives an input optical beam that is part of the light carried by the optical communication system. The WSS 211 or a divider, such as divider 121 in fig. 2, may be used to separate the optical beam from the fast channel (fig. 3). Referring to fig. 4, the distributor 321 divides the received light beam into N sub-beams and provides them to an output port of the distributor.

The splitter 321 may be preceded by an optional optical amplifier 32 (fig. 3) that amplifies the input beam before it is provided to the input port of the splitter 321. The distributor 321 may be followed by amplifiers 332, the amplifiers 332 being connected to receive a plurality of sub-beams from the distributor 321, each amplifier 332 receiving one sub-beam for amplifying a particular sub-beam. In other words, the divider 321 and the amplifiers 32 and/or 332 form a dividing circuit 380 that performs power division and amplification.

In one embodiment,

amplifiers

32 and 332 may be used in the same circuit, such that the beams are amplified before splitting and the sub-beams are amplified after splitting. In another embodiment, the distribution circuit 380 includes cascaded power dividers. For example, at least some and preferably all of the sub-beams provided at the output ports of the splitter 321 may be amplified by one of the amplifiers 332 and may be further split by a secondary power splitter and may be further amplified. In other words, the power splitting circuit 380 includes at least one optical power splitter for receiving the optical beam at an input port of the power splitting circuit, splitting the optical beam to obtain a plurality of sub-optical beams, and providing the plurality of sub-optical beams to an output port of the power splitting circuit. Optical power splitters are known in the industry and are commercially available. In one embodiment, power distribution circuit 380 may be replaced with amplifier 32.

One or more switching circuits 381 may be provided after the distribution circuit 380. Each switch module 381 on the drop side of the module includes a multicast-and-select (MCS) switch 340 having a plurality of input ports and a plurality of output ports.

One or more of the input ports of each MCS switch 340 may be coupled to an output port of a distribution block, wherein one input port of the switch may receive one of the sub-beams provided at an output port of a distribution circuit 380 (also referred to herein as a distribution block 380). In one embodiment, the number of switches is equal to the number of sub-beams provided by the distribution block. Alternatively, MCS switch 340 may receive an input beam from WSS 21, where the beam may be amplified by amplifier 32. In other words, the allocation block 380 is optional.

MCS switches (e.g., switch 340) are known in the art of optical communications. Fig. 5 is a schematic diagram of the MCS switch. On the drop side, the multicast selection switch may include a plurality of distributors 410, the distributors 410 multicasting the sub-beams received at the input ports 420. Each switch 430 may direct light received at one of the input ports 420 to one of the output ports 440. In a particular embodiment, the switch has 8 input ports and 16 output ports. Of course, the number of ports of the MCS switch may vary.

The switch circuit 381 on the drop side of the module also includes a plurality of light selective devices 350, each light selective device 350 for blocking some wavelengths of light from passing therethrough and for passing at least one wavelength of light therethrough to provide an output to an output port of the selective device. Each selective device 350 may select a particular channel that allows for a certain wavelength or a range of wavelengths. Each of the selective devices 350 has an input port optically coupled to one of the plurality of output ports of the MCS switch. Typically, each selective device 350 (also referred to as a selective component or element) has a single input port and a single output port.

The selective device 350 may be used to select one or more desired channels that are intended to be dropped on a given port and block undesired channels. This allows the use of coherent receivers and/or direct detection receivers that require per-channel filtering. The selectivity device may be a tunable filter (as discussed further with reference to fig. 6) or a trap. The selective device may be reconfigurable or tunable so that one or more wavelengths selected to pass may be changed. The selective device increases the flexibility of the add/drop system that can be reconfigured at the MCS switch as well as at the selective device 350.

Preferably, the plurality of selective devices 350 includes a Wave Blocker (WB) array. A wave trap is an optical module that allows a selected wavelength or wavelengths to pass through and blocks all other undesired wavelengths. "blocking" is understood to include substantial attenuation of the undesired portion of the spectrum, at least by 10 dB.

The wave trap may be a channelized wave trap that only allows specific channel sizes and spacings, or may be a flexible grid wave trap to enable selected channels of any size and spectral position to have a specific frequency granularity. The array of wave traps may be formed from a plurality of single chip devices packaged together into a single package or from a multi-channel chip that can support the desired number of channels in the array.

The wave trap may comprise a dispersive element that separates the optical signal according to wavelength in free space, e.g. a grating or prism, or into different waveguides, e.g. by an Arrayed Waveguide Grating (AWG). The wave trap may include an optical directing element, such as a liquid crystal on silicon (LCoS), a micro-electromechanical mirror (mems) array, a Liquid Crystal (LC) switch array, or the like, to direct selected signals to the second dispersive element so that the second dispersive element can recombine the signals and pass them into the output optical port. Typically, the first and second dispersive elements are the same piece of grating or one or more prisms in common.

Any wave trap operating in the C or L band, i.e. between 1530 nm and 1625 nm, may be used as the selectivity device 350.

Drop-side switch module 381 also includes a plurality of amplifiers 360, each connected to one of the plurality of filters, and may form an amplifying array for amplifying the output beam. The amplifiers of the add/drop modules, such as

amplifiers

331, 332, 360, and 361, are preferably erbium-doped fiber amplifiers (EDFAs), although any other type of amplifier may be used. The output port of the amplifier may be coupled to a receiver 41. In some embodiments, amplifier 360 may be omitted.

Advantageously, the add/drop module disclosed herein can support a greater number of TRs for the same number of add/drop ports on WSSs 20 and 21 (fig. 3) than conventional add/drop modules. In this example, the power splitter 321 is shown with a splitting ratio (splitting ratio) of 1 × 2, however, other power splitting ratios, for example, from 2 to 8, may also be used. A higher power splitting ratio enables an increase in the number of TRs 40 that can be supported at the expense of a slight increase in the decrease in the optical signal-to-noise ratio on the dropped path due to increased losses in the power splitter. The selective device 350 reduces noise by blocking unwanted wavelengths and selecting only the desired wavelengths.

In operation, in a selection and selection architecture, one or more WSS switches 20 and 21 (fig. 3) may select M optical beams from light propagating through an optical communication system. After selecting the M beams, each of the M beams may be assigned using M power splitters, such as splitter 321 (fig. 4), with different splitters assigning different channels. The splitter 321 may be a 1 × N splitter providing N sub-beams at the output port of each splitter, for a total of N × M sub-beams, each sub-beam being possible to be directed by one of the MCS switches 340 to one of the wave traps 350 in order to be able to provide a specific wavelength or a narrow range of wavelengths to a specific receiver 41. For example, N may be 2, 4 or 8. M may be 1 to Mmax, where Mmax is limited to the available WSSs, while the maximum number of WSS ports currently available is 32. Each MCS switch may be coupled to receive one or more sub-beams from a particular splitter 321. In one embodiment, the nxm sub-beams may be switched by N switches 340, where each switch is coupled to receive M sub-beams, one from each of the M dividers 321. In another embodiment, one of the MCS switches may be coupled to receive more than one sub-beam from a particular splitter 321. The output port of the switched MCS switch may be coupled to a selective device 350, which selective device 350 may select a particular channel (wavelength) for further amplification by the amplification array 360 and provide an output beam to the receiver 41. Of course, the optical beams may be amplified at various locations on the drop side of the ROADM module 230 within the modules 380 and 381 (fig. 4).

Drop-side optical amplification array 360 may include a plurality of segments, also referred to herein as optical amplifiers, each segment having an input port optically coupled to one of selective devices 350 for receiving an optical signal to be amplified. Each segment has one or more rare-earth doped fibers (i.e., a sheet of optical fiber) for amplifying an optical signal propagating therethrough. The amplifier (segment) has an output port for providing an amplified optical signal. The optical amplification array may comprise one or more laser pumps (laser pumps) for providing pump light sufficient to fully saturate all rare earth doped fibers in the optical amplification array, wherein the number of laser pumps is smaller than the number of optical amplifiers. At least some of the optical amplifiers may each have a pump light port for receiving at least a portion of the pump light from one or more laser pumps or from another of the optical amplifiers (segment). Preferably each segment of the array has a laser pump port for receiving at least a portion of said pump light. Such an amplification array, in which the rare-earth doped fiber can be fully saturated with pump light, is referred to herein as an over-pumped array and is discussed further with reference to fig. 10-12. The add-drop side of the add-drop module may also include such an enlarged array.

In operation, in the broadcast and selection architecture, a splitter positioned as splitter 120 (fig. 2) taps an optical beam that includes all wavelengths propagating through the optical communication system. Another splitter 321 (fig. 4) may split the input beam into sub-beams. Each of the one or more MCS switches 340 has a plurality of input ports, wherein one or more of the input ports are coupled to an output port of the splitter 321 to receive one or more of the sub-beams and direct the sub-beams to an output port of the switch, each of the output ports being optically coupled to one of the plurality of selective devices 350, such that a particular wavelength or range of wavelengths can be provided to a particular receiver 41 coupled to an output port of one of the selective devices 350. Likewise, the optical beams may be amplified at various locations on the drop side of the ROADM module 230 within modules 380 and 381 (fig. 4).

Thus, the add/drop module disclosed herein may be used in selection and selection architectures as well as broadcast and selection architectures.

In these examples, splitter 321 may be replaced with a splitter circuit comprising a cascade of several power splitters, as discussed above.

With further reference to fig. 4, the insertion side of the add/drop module 230 is shown in the left half of the figure.

On the add side, an over pumped (over pumped) amplifier array may be used at the input, coupled to the input port of the add/drop module, which is used to connect the transmitter 42. Since each of these amplifiers only needs to support one or more channels from a single transmitter, the complexity and required pump power is greatly reduced compared to multi-wavelength amplifiers. The selective device behind the input amplifier can equalize the channel power and also block any unwanted ASE (amplified spontaneous emission) from the input amplifier, if desired. Placing the optical amplifier 361 at the input of the add/drop architecture as shown in fig. 4, rather than behind the MCS as in conventional designs, relaxes the output power requirements for the transmitter and significantly improves noise performance.

Referring to fig. 4, the plug-in side of the module includes one or more switching circuits 370 and an optional combining circuit 371. At least some of the input ports of switching circuitry 370 may be coupled to receive input sub-beams from transmitters 42 (fig. 3), where each transmitter may have a tunable laser that may be dynamically routed in any direction at any wavelength without collision with other wavelengths. Switching circuit 370 may include a plurality of input amplifiers 361, preferably in an array, wherein each amplifier is coupled to receive an input sub-beam from one of emitters 42.

Each of the plurality of light selective devices 351 may be coupled to receive an amplified input sub-beam from one of the amplifiers 361. The wavelength selective device 351, such as a trap, attenuates out-of-band noise, including Amplified Spontaneous Emission (ASE) from other amplifiers. Since the received sub-beams may be combined at the switch 341 and the one or more combiners 320, the noise introduced by the amplifier 361 will be combined and further amplified by the other amplifiers. Selective device 351 allows only the desired channel to pass through and may be implemented in the same manner as selective device 350 on the drop side. In particular, the selectivity device 351 may comprise a tunable optical filter and/or a filter comprising a selective absorber. The selective devices 351 at the insertion side are optional, but their use provides the advantage of improved optical signal to noise ratio (OSNR) performance. As shown in fig. 6, the initial amplifier 361 is also optional, i.e. if the output power of the transmitter 42 is sufficiently high, the amplifier 361 is not required.

The switching circuit 370 includes one or more MCS switches 341. The input ports of the MCS switch 341 are optically coupled to receive input sub-beams from the transmitter 42 (fig. 3), wherein the input sub-beams may be amplified by an amplifier 361 and/or filtered by a wave trap and/or filter 351 on the way between the transmitter 42 and the input ports of the MCS switch 341. The output port of the MCS switch 341 may be optically coupled to the amplifier 331.

Fig. 5 shows the insertion-side MCS switch 341 (fig. 4). Port 440 serves as an input port of the MCS switch at the add side of the add/drop module and port 420 serves as an output port. The add/drop MCS switches preferably have the same size. Fig. 5 shows an 8 × 16 MCS switch as an example.

The power divider or dividers 320 acting as optical combiners preferably have the same ratio as the divider or dividers 321 on the drop side. Each MCS switch 341 may direct each received input sub-beam to an output port of the switch that is coupled to one of the splitter/combiners 320. For example, the insertion side of module 230 provides two input beams as shown in FIG. 3, one directed to WSS 23 and the other directed to WSS 22. Thus, in this example, the combiner module 371 (fig. 4) includes two dividers/combiners 320. The divider/combiner 320 and the amplifier 331 may be part of a combining circuit 371. Alternatively, one or more dividers 320 may be omitted and combining circuit 371 may be reduced to amplifier 331, then amplifier 36 is not required.

Fig. 6 illustrates an exemplary embodiment of the add/drop module structure disclosed herein with reference to fig. 4. WSS switches 620 and 622 correspond to WSS switches 20 and 22 (fig. 3). WSS switches 620 and 622 are shown as 1 x 9 WSS, however this configuration is applicable to WSS modules of any size.

On the drop side, on the left side of the figure, one or more input beams may be provided to the add/drop system. Although 4 beams are shown, a different number of beams may be selected by WSS 620 and/or 622.

The exemplary add/drop implementation includes optical amplifiers 632, each for amplifying one of the input beams. Each amplifier 632 is optically coupled to one of the power dividers 621. The module also includes one or more multicast selection switches 640 (shown, for example, in fig. 6), and a plurality of selective devices in the form of Tunable Optical Filters (TOF) 650 for blocking light beams of some wavelengths from passing through the selective devices and passing light of at least one other wavelength through the selective devices to provide output light beams to output ports of the selective devices.

Any tunable filter operating in the C or L band, including grating-based, electromechanical or microelectromechanical system (MEMS) based etalons, waveguide Mach-Zehnder interferometers, and fiber rings, may be used as the selectivity device in the add/drop module 230. Tunable filters typically pass (or block) a single wavelength or a set of adjacent wavelengths with a bandwidth of up to 5 nm.

The module shown in fig. 6 also includes an array of optical amplifiers 660, shown as amplifiers 360 in fig. 4.

As shown in fig. 6, the amplifier 632 may be located before the distributor 621 along the optical path of the drop channel. Alternatively, amplifier 632 may be replaced or used concurrently with multiple amplifiers located after divider 621 (as amplifier 332 (fig. 4) is located after divider 321). In other words, the drop side of the allocating module 625 comprises an allocator 632 for allocating dropped channels and one or more amplifiers 621 for amplifying extracted channels before and/or after allocation, wherein the allocator and amplifiers form an allocating circuit, as discussed above. The assignment module 625 may be implemented in the OPS-4 card as shown in fig. 6.

In the example shown in fig. 6, the insertion side is free of filters or wave traps such as shown in fig. 4. The module may comprise one or more MCS switches, e.g. MCS switch 641, the MCS switch 641 followed by an optical amplification array 661, followed by a power splitter 635 (preferably in the same ratio as the splitter 621 on the drop side), followed by an optical amplifier 645.

Various embodiments of the add/drop modules disclosed herein may include several splitters and amplifiers along each optical path. However, different wavelengths may not be amplified by the same factor. Fig. 7 shows a typical gain spectrum of an EDF (erbium-doped fiber) amplifier. This spectrum presents various problems including increased cross-talk. It is therefore desirable to be able to flatten the gain spectrum of a particular amplifier or distributed amplifier along each optical path in an add/drop system. In other words, it is desirable that the total gain from the drop port to the receiver be the same for all wavelengths. It is also expected that the total gain from the receiver to the add port should be the same for all wavelengths.

The amplifiers on the drop path may be designed as distributed amplifiers with gain compensation. Fig. 8 provides an example in which the gain profile 810 of the first optical amplifier 820 is designed to compensate for the gain profile 830 of the final amplifier 840, which may be a segment of an amplifier array coupled to receive a sub-beam from one of the selective devices 350 (fig. 4). The spectrum 810 of the first amplifier 820 has a positive slope and the spectrum 830 of the second amplifier 840 has a negative slope, while the overall gain spectrum is flat. The first optical amplifier 820 may include a gain balancing filter 850, the gain balancing filter 850 being designed to compensate for gain non-uniformity along each optical path on the drop side of the module. Gain balancing (or compensation) can be achieved by using yttrium co-doped amplification waveguides. The first optical amplifier 820 shown in fig. 8 may correspond to one of the amplifiers 32 (fig. 3) or 332, or a combination thereof. In other words, all of the amplifiers along each drop path are combined together and configured to balance the gain along each path. The gain compensation filter (also referred to herein as a gain flattening filter) may be part of amplifier 32 (fig. 3) and/or amplifier 332.

Referring to fig. 4 and 8, in one embodiment, the optical system may include a drop-side optical circuit, such as circuit 381. The circuit includes an MCS switch, such as switch 340, having a plurality of input ports and a plurality of output ports. The circuit also includes selective devices, such as device 350, each for blocking the passage of light at some wavelengths therethrough and for passing light at least one other wavelength therethrough to provide an output to an output port of the selective device. Preferably, each of the selective devices has a single input port optically coupled to an output port of the MCS switch, and a single output port that may be coupled to the receiver 41. Alternatively, the drop-side optical circuit may further comprise an output amplifier, such that the output port of one of the selective devices is coupled to one of the amplifiers, which may be, but need not be, part of an over-pumped amplification array.

The output amplifier coupled to the selective device is shown in amplifier 840 (FIG. 8). The drop-side optical circuit may also include an input amplifier optically coupled to the input port of the MCS switch and shown in amplifier 820, including a GFF (gain flattening filter) configured for gain balancing along all drop paths in the drop-side optical circuit, where the GFF is a single GFF in the first drop-side optical circuit.

The system may also include a distribution circuit and further drop-side optical circuits, as discussed above with reference to fig. 4. Each of the one or more input amplifiers may include a GFF, such as GFF 850.

The add-side amplifier may also be designed to balance the gain on all optical paths on the add side of the module. Fig. 9 provides an example in which the gain profile 910 of a top-most (top) optical amplifier 920 includes a GFF 950 designed to compensate for the gain curve 930 of the amplifier segment 940 in an amplifier array, which may be implemented in a cascaded fashion as shown in fig. 11 and 12. Gain balancing (or compensation) can be achieved by codoping the amplifying waveguide or block with yttrium. The optical amplifier 920 of the tip shown in fig. 9 may correspond to one of the amplifier 36 (fig. 3) or the amplifier 331 (fig. 4), or a combination thereof. In other words, all of the amplifiers along each drop path are combined together and configured to balance the gain along each path. The gain compensation filter (also referred to herein as a gain flattening filter) may be part of amplifier 36 (fig. 3) and/or amplifier 331. The distributed nature of the amplification on the insertion side also results in improved OSNR performance and lower cost when compared to conventional designs.

The gain balancing approach may be combined with the use of an over-pumped amplifier array, as discussed further below. However, the two methods may be used separately.

Returning to the drop side of the module shown in fig. 6, the TOF bandwidth can be chosen to be in the range of a few nanometers (e.g., 5 nanometers), which allows for low cost manufacturing while still filtering out most of the optical power and passing only the desired channel.

In general, the wavelength range through the trap does not have to be as narrow as the bandwidth of the TOF. However, the add/drop module 230 includes a filter for selecting a single wavelength channel or a super channel, which is typically characterized by a narrow bandwidth. In other words, each selective device including a wave trap preferably has a narrow bandwidth, or can be configured to have such a bandwidth. If the wave trap passes light energy in several wavelength ranges, their cumulative bandwidth is still narrow.

Thus, after being allocated in numbers and provided only one or more narrow portions of the spectrum, the final optical amplifier array 660 (FIG. 6) and array 360 (FIG. 4) need only support low power inputs with any selective device 350.

Advantageously, the add/drop system is compatible with a super channel, which may be a combination of multiple individual channels to support a higher bandwidth TR. The narrow bandwidth reduces the optical power loaded into the final amplifier and hence into the receiver, which also reduces out-of-band noise provided to the receiver, solves the problem of receiver overload, and improves the noise performance of the receiver. Since the final

optical amplifier array

360 or 660 need only support low power inputs through filtering by the selective device 350, an over-pumped amplifier array can be used to greatly simplify the design and reduce cost.

Fig. 10 shows an example of an over-pumped amplifier array for the drop side. Two laser pumps 880 and 882 are connected on either side of a cascade consisting of 16 short pieces (short pieces) of rare earth doped fiber 870, preferably Erbium Doped Fiber (EDF). In one embodiment of the array, only one pump is used. In other embodiments, there may be more than two pumps, however fewer than amplifiers 870. Sharing pump power among multiple amplifiers simplifies design and reduces cost.

The light amplification arrays, such as array 660 (FIG. 6) and array 360 (FIG. 4), include a plurality of light amplifiers. Each amplifier has an input port optically coupled to one of the selective devices shown in devices 350 (fig. 4) and 650 (fig. 6) for receiving an optical signal to be amplified. In this and other scenarios, a port may be any connection, including a cross section of optical fibers, couplers, combiners, etc. Each amplifier may include one or more rare earth doped fibers 670 for amplifying optical signals propagating therethrough. In operation, an amplified optical signal is provided to the output of the amplifier. Further, each amplifier may have a pump light port for receiving at least a portion of pump light from one or more laser pumps or from another optical amplifier of the plurality of optical amplifiers.

In operation, the one or more laser pumps provide a constant pump light sufficient to fully saturate all of the rare-earth doped fibers 670 in the optical amplification array. In one embodiment, the length of each of the erbium doped fibers and the concentration of erbium ions are such that when the fibers are fully saturated, each amplifier provides less than 15dB of amplification to the signal to be amplified when passing through each amplifier.

Due to the high pump power relative to the signal power, the optical amplifier operates in a linear state and the average gain across all wavelengths is fixed without the need for any complex control circuitry. Referring to fig. 10, the first (upper left) amplifier receives pump light from the pump 880 via a dichroic mirror 881, which serves as the pump light input port of the first amplifier. A dichroic mirror 872 is used to direct the remaining pump power from the first amplifier to the second amplifier; the mirror 872 serves as a pump light output port in the first amplifier. A dichroic mirror 874 serves as a pump light input port in the second amplifier. An optical signal (sub-beam) received at an input port of a specific amplifier propagates from the input port to an output port of the amplifier while being amplified, without being substantially guided to another amplifier, unlike pump light.

In some cases, a single Gain Flattening Filter (GFF) may be used in amplifier 332 (fig. 4) or amplifier 32 (fig. 3) to achieve gain flattening on all possible drop paths. This eliminates the need for GFF in each amplifier segment of the amplifier array 360 (or in some embodiments multiple individual final amplifiers), further reducing cost and complexity. Distributing the gain in this way also reduces the OSNR degradation of the drop structure and reduces the required output power of the first amplifier. The end result of this design is a higher performance, lower cost drop-out structure than conventional designs.

Referring to fig. 3 and 4, the array 360 is preferably an over-pumped array as described above, however other types of amplifiers 360 may be used. If the add/drop module includes amplifier 32 and/or amplifier 332, each of these amplifiers may include a GFF for flattening the gain spectrum in the drop side of the add/drop module.

Fig. 11 provides an example of an over-pumped add-side amplifier array. Similar to the drop side, the two

counter-propagating pumps

884 and 886 provide a high level of pump power relative to the signal power in each amplifier segment, which results in a fixed gain and no need for control circuitry.

Pumps

884 and 886 are connected in a cascade consisting of 16 short pieces of erbium (erbium) optical fiber, such as optical brazing sheet 888. Due to the high pump power relative to the signal power, the optical amplifier operates in a linear state and the gain of the optical amplifier is fixed without the need for any complex control circuitry. The array may include a dichroic mirror 890 to share gain power between the multiple output sub-beams provided by the multiple TOF or wave-traps, as discussed above with reference to fig. 10. Optical signals (sub-beams) received at an input port of a particular amplifier are provided, amplified to an output port of that amplifier, and not substantially directed into another amplifier, unlike pump light.

Turning now to fig. 12, an amplification array is shown in which a single high power laser diode pump provides constant, non-varying light to the amplification section.

The amplification array includes a plurality of amplifiers. In fig. 12, the indices a to n simply indicate n inputs through the same optical element, or in other words, n amplifiers. The amplification array comprises an isolator 102a, a laser diode optical pump 104 labeled LD and an isolator 116a, the laser diode optical pump 104 and the isolator 102a being coupled together by a Wavelength Division Multiplexer (WDM) 106 a. Block 702a represents a plurality of short EDF sections coupled in series with an optional distributed gain flattening medium (also referred to as the gain flattening filter discussed above). WDM 430a is provided to remove any remaining pump signals.

It should be noted that in fig. 12, the pump signal provided by the laser diode 104 is extracted at WDM 430a and routed into input b of the amplification array for amplification of the b-th input signal. It can be seen that the pump signal is removed and recycled down to each subsequent input line of the amplification array. In this manner, n input signals are amplified and filtered by n GFF + EDF modules 705a through 705 n. In this regard, perhaps the term "over saturation" may be best understood because if the EDF within 705n is to be fully saturated, the constant power pump signal must have more output power than required to fully saturate the EDF within module 705a, since the remaining unused tapped 980 nm pump light is directed to the next amplification input line from 1 st to nth.

In the examples shown with reference to fig. 10 and 11, each array comprises two laser pumps, whereas in the example of fig. 12 there is one pump. In other words, the amplification array may comprise one or more pumps, and the number of pumps may be kept low, less than the number of amplifiers in the array, which will reduce costs. The power of the pump light provided by the pump or pumps should be sufficient to saturate the rare-earth doped fiber, i.e. greater than the power that the fiber can absorb, which can be easily calculated from the total length of the doped fiber and the rare-earth ion concentration.

The add-side amplifier can be designed to achieve gain flatness across all add paths while requiring only one GFF in the top amplifier, as shown in fig. 9. The requirement for gain flattening is relaxed due to the channel equalization capability of the wave trap. In embodiments where multiple amplifiers 331 are used between the MCS switch 341 and one or more dividers 320, each amplifier 331 may include a GFF filter. Amplifier 36 may also include a GFF filter.

The embodiments may be modified to configure the add/drop modules disclosed herein, depending on the performance and cost tradeoffs required for a particular application. For example, the power splitter 321 at the input of the drop structure and the power splitter 320 at the output of the add structure may be omitted. This may improve optical signal-to-noise ratio and reduce cost when the optical communication system has a sufficient number of add/drop ports on WSS 21 and does not require port aggregation provided by the power splitter.

Depending on the noise performance requirements and the power level requirements of the in and out add/drop structure, there may be no input amplifier 32 (fig. 3) or amplifier array 332 (fig. 4) on the drop side. This configuration may reduce cost, size, and power for applications that do not require the performance level of the complete architecture shown in fig. 4.

Finally, on the add side, if the performance requirements are relaxed, there may be no input amplifier array 361 and no filter resistor 351 or output amplifier 36 (fig. 3) on the add side. This, in turn, may reduce cost, size, and power requirements for applications that do not require the performance levels of the embodiment shown in fig. 4. Since the maximum output power of an over-pumped amplifier is limited (less than 12dBm to maintain constant gain), other types of amplifiers can be used for the add path if higher output power is required.

Advantageously, the proposed add/drop module supports a larger number of add/drop TRs than the conventional design. The add/drop system disclosed herein provides better OSNR performance due to noise rejection of the trap or filter, and also provides better isolation compared to competing nxm WSS technologies. The solution disclosed herein also enables a conflict-free and offers all these advantages at a lower cost compared to competing designs. The add/drop architecture disclosed herein is compatible with WSS blocks that use power splitters or WSS modules on the lines on one side. It is therefore suitable to be deployed as an upgrade to existing ROADM deployments, where most existing ROADM deployments use a power splitter on the lines on one side. In addition, since fewer WSS ports are needed for add/drop, higher degree nodes can be supported with lower port count WSS modules, further extending the utility of lower cost and lower port count WSS modules.

It is noted that the drop-side optical circuit and the add-side optical circuit of any embodiment may be connected together in the same optical system, or may be separate devices, and only one may be used in a particular case.

While the invention will be described in conjunction with various embodiments and examples, it is not intended to limit the invention to these embodiments. On the contrary, the invention covers various alternatives, modifications and equivalents, as will be appreciated by those skilled in the art.

Claims

1. An optical system comprising a first drop-side optical circuit, the first drop-side optical circuit comprising:

a multicast selection MCS switch having a plurality of input ports and a plurality of output ports;

a plurality of selective devices, each selective device for blocking light of some wavelengths from passing therethrough and for passing light of at least one other wavelength therethrough to provide an output to an output port of the selective device, wherein each of the plurality of selective devices has an input port optically coupled to an output port of the MCS switch; and

an optical amplification array comprising a plurality of optical amplifiers, each optical amplifier having an input port optically coupled to one of the selective devices for receiving an optical signal to be amplified, wherein each of the plurality of optical amplifiers comprises one or more rare-earth doped optical fibers and has an output port for providing an amplified optical signal, the optical fibers for amplifying the optical signal propagating therethrough;

Wherein the optical amplification array has a single laser pump or two counter-propagating laser pumps for providing constant pump light sufficient to fully saturate all rare-earth doped fibers in the optical amplification array and for making the optical amplification array an over-pumped amplifier array;

wherein each of at least some of the optical amplifiers has a pump light port for receiving at least a portion of pump light from the single laser pump or the two counter-propagating laser pumps or from another of the optical amplifiers;

wherein at least one of the optical amplifiers is connected to receive a portion of the pump light from the other optical amplifier; and

wherein the first drop-side optical circuit comprises an input amplifier optically coupled to an input port of the MCS switch, wherein the input amplifier comprises a gain flattening filter GFF.

2. The optical system of claim 1, wherein the plurality of selective devices comprise a wave trap or a tunable filter.

3. The optical system of claim 2, comprising an add-on-side optical circuit, wherein the add-on-side optical circuit comprises:

(a) An add-side optical amplification array comprising a plurality of optical amplifiers, each optical amplifier having an input port for receiving an optical signal to be amplified;

wherein each of the plurality of optical amplifiers comprises one or more rare-earth doped optical fibers for amplifying optical signals propagating therethrough and has an output port for providing amplified optical signals;

wherein the insertion-side optical amplification array has a single laser pump or two counter-propagating laser pumps for providing constant pump light sufficient to fully saturate all rare-earth doped fibers in the optical amplification array, and for making the insertion-side optical amplification array an over-pumped amplifier array, and for making the optical amplification array an over-pumped amplifier array;

wherein each of at least some of the optical amplifiers of the insertion-side optical amplification array has a pump-light port for receiving at least a portion of the pump light from the single or the two counter-propagating laser pumps of the insertion-side optical amplification array or from another of the plurality of optical amplifiers of the insertion-side optical amplification array;

Wherein the add-on-side circuit further comprises:

a plurality of add-side selective devices, each for blocking the passage of some wavelengths of light therethrough and for passing at least one other wavelength of light therethrough to provide an output to an output port of the selective device, wherein each of the plurality of add-side selective devices has an input port optically coupled to the output port of one of the plurality of amplifiers in the add-side optically amplified array; and

an add-side multicast select switch having a plurality of input ports and a plurality of output ports, wherein each of the plurality of input ports is optically coupled to an output port of one of the plurality of add-side selective devices; or

(b) An insertion side MCS switch and an amplifier coupled to an output port of the insertion side MCS switch.

4. The optical system of claim 2, wherein the first drop-side optical circuit comprises: a first power splitting circuit comprising one or more power splitters and one or more amplifiers, wherein the first power splitting circuit has an input port and an output port, and wherein one or more of the output ports of the first power splitting circuit are optically coupled to one or more of the plurality of input ports of the MCS switch.

5. The optical system of claim 4, wherein the input port of the first power splitting circuit is:

(a) an input port of one of the one or more amplifiers, wherein an output port of the amplifier is optically coupled to an input port of one of the power dividers, or

(b) An input port of one of the power dividers, wherein each output port of the power divider is coupled to an input port of one of the one or more amplifiers.

6. The optical system of claim 4, wherein each of the one or more amplifiers comprises:

(a) a gain flattening filter; or

(b) One or more rare-earth doped optical fibers configured to balance gain along each drop optical path in the first drop-side optical circuit.

7. The optical system of claim 4, comprising a second drop-side optical circuit;

wherein the second drop-side optical circuit includes:

wherein the optical amplification array of the second drop-side optical circuit has a single laser pump or two counter-propagating laser pumps for providing constant pump light sufficient to fully saturate all rare-earth doped fibers in the optical amplification array and for making the optical amplification array an over-pumped amplifier array;

wherein each of at least some of the optical amplifiers of the optical amplification array has a pump light port for receiving at least a portion of the pump light from the single laser pump or the two counter-propagating laser pumps of the optical amplification array or from another optical amplifier of the plurality of optical amplifiers of the optical amplification array; and

Wherein one or more of the plurality of input ports of the MCS switch of the second drop-side optical circuit are coupled to one or more of the output ports of the first power distribution circuit.

8. The optical system of claim 7, comprising a second power splitting circuit comprising one or more power splitters and one or more amplifiers, wherein the second power splitting circuit has an input port and an output port;

wherein one or more of the plurality of input ports of the MCS switch of the first drop-side optical circuit are coupled to one or more of the output ports of the second power distribution circuit, and wherein one or more of the plurality of input ports of the MCS switch of the second drop-side optical circuit are coupled to one or more of the output ports of the second power distribution circuit.

9. An optical system includes an insertion side-light circuit;

wherein the add-side optical circuit comprises an add-side optical amplification array comprising a plurality of optical amplifiers, each optical amplifier having an input port for receiving an optical signal to be amplified;

wherein the insertion-side optical amplification array has a single laser pump or two counter-propagating laser pumps for providing constant pump light sufficient to fully saturate all rare-earth doped fibers in the insertion-side optical amplification array and for making the optical amplification array an over-pumped amplifier array;

wherein each of at least some of the optical amplifiers in the insertion-side optical amplification array has a pump-light port for receiving at least a portion of the pump light from the single or the two counter-propagating laser pumps of the insertion-side optical amplification array or from another of the plurality of optical amplifiers of the insertion-side optical amplification array;

wherein at least one of the optical amplifiers is connected to receive a portion of the pump light from the other optical amplifier;

wherein the add-on-sidelight circuit further comprises:

a plurality of add-side selective devices, each for blocking the passage of some wavelengths of light therethrough and for passing at least one other wavelength of light therethrough to provide an output to an output port of the selective device, wherein each of the plurality of add-side selective devices has an input port optically coupled to the output port of one of the plurality of amplifiers in the add-side optically amplified array;

An add-side multicast select switch having a plurality of input ports and a plurality of output ports, wherein each of the plurality of input ports is optically coupled to an output port of one of the plurality of add-side selective devices; and

wherein the add-side optical circuit comprises a gain flattening filter GFF.

10. The optical system of claim 9, further comprising: another add-side optical circuit and a combining circuit comprising a power splitter and one or more amplifiers, wherein an input port of the combining circuit is coupled to receive light from both add-side optical circuits.